Mobile communications devices use antennas for radio frequency wireless communication with terrestrial electromagnetic signal sources, such as cellular network base stations, Wi-fi access points and Bluetooth beacons. The strengths of signals received by the antennas from such electromagnetic signal sources vary greatly in dependence on the spatial relationship between the mobile device and the signal source. The received signal strength is typically a function of distance and direction of the mobile device from the electromagnetic signal source, but the function can be more complex when obstructions are provided in the line of sight between the mobile device and the electromagnetic signal source, and when multi-path propagation occurs, for example due to signal reflections.
In order to reduce interference, and therefore improve transmission and reception of electromagnetic signals by the antennas, it is known to provide a directional antenna and to steer the antenna in the direction of the electromagnetic signal source. However, when mobile devices move, the antenna often needs to be steered back towards the electromagnetic signal source to maintain a wireless communications link of the required quality. This can require the antenna to perform a scan by (electronically or mechanically) steering the principal communication direction of the antenna across a range of directions in order to determine an optimum principal communication direction along which to communicate with the electromagnetic signal source, particularly when the antenna is not initially in communication with the electromagnetic signal source (which may require the scan to be performed over a larger range). This scanning process typically takes time and uses a significant quantity of battery power.
Accordingly a new way of steering steerable directional antennas, which reduces the battery power consumption, is required.